1. Field of the Invention
The present invention relates to a telephone controller for VoIP.
2. Description of the Related Art
A conventional telephone service using a part or all of a communication line for packet communication, especially, a telephone service for packet communication over the Internet (IP network), is called VoIP (Voice over IP). Unlike a conventional line switching procedure for a line switched network, VoIP is based on TCP/IP. A telephone also makes a call based on TCP/IP. That is, a calling telephone sends voice information, split into packets based on TCP/IP, to a receiving telephone. On the other hand, communication via VoIP requires the management of global IP addresses allocated to the telephones. This is because a global IP address must be globally unique.
A rapid increase in the number of Internet terminals produces some problems; for example, the available global IP addresses become insufficient, and an increased number of globally-registered IP addresses makes the management of global IP addresses more complex. For example, when a plurality of telephones are connected to the Internet via a LAN, it is difficult to allocate a globally-unique IP address to each telephone in the LAN.
To solve this problem, a private IP address is assigned to each telephone in a LAN and the address is converted between the private IP address and the global IP address. This method requires a router with the network address translator (NAT) function to be installed between the LAN and the Internet to allow the NAT to translate the private IP address of each telephone to a global IP address. This router, however, prevents external units from directly accessing the terminals in the LAN to ensure security. This mechanism is called a firewall. Therefore, the NAT function, once installed, allows a telephone in the LAN to make a call to an external telephone over the Internet but prevents an external telephone connected to the Internet from directly making a call to a telephone in the LAN. That is, although some persons outside the LAN should be allowed to make a call to a telephone in the LAN, the conventional system does not allow it. In addition, an external person cannot make a call to a telephone in the LAN over the Internet even if he or she who knows its private IP address because the address is not registered with the Internet.